1. Field of the Invention
This invention relates to a motor control device and a motor control method, and more particularly, to a motor control device and a motor control method for stop position predictive control of at a terminal portion of a deceleration control period.
The invention also relates to a motor control device and a motor control method for paper feed control of a printer enabling a print over a wide area of a sheet including portions nearest to ends of the sheet.
The invention further relates to a recording medium having recorded a computer program for executing any of those motor control methods.
2. Related Background Art
First explained is general configuration of an ink jet printer using a motor control device and its control method.
FIG. 1 is a block diagram that shows general configuration of an ink jet printer.
The ink jet printer shown in FIG. 1 includes a paper feed motor (hereinafter also called a PF motor) 1 that feeds paper; a paper feed motor driver 2 that drives the paper feed motor 1; a carriage 3 that supports a head 9 fixed thereto to supply ink onto printing paper 50 and is driven to move in parallel to the printing paper 50 and vertically of the paper feeding direction; a carriage motor (hereinafter also called a CR motor) 4 that drives the carriage 3; a CR motor driver 5 that drives the carriage motor 4; a DC unit 6 that outputs a d.c. current for controlling the CR motor driver 5; a pump motor 7 that controls the draft of ink for the purpose of preventing clogging of the head 9; a pump motor driver 8 that drives the pump motor 7; a head driver 10 that drives and controls the head 9; a linear encoder 11 fixed to the carriage 3; a linear encoder coding plate 12 having slits in predetermined intervals; a rotary encoder 13 for the PF motor 1; a paper detecting sensor 15 that detects the terminal position of each sheet of paper under printing; a CPU 16 that controls the whole printer; a timer IC 17 that periodically generates interruption signals to the CPU 16; an interface portion (hereinafter also called IF) 19 that exchanges data with a host computer 18; an ASIC 20 that controls the character resolution, driving waveform of the head 9, and so on, in accordance with character information sent from the host computer 18 through the IF 19; a PROM 21, a RAM 22 and an EEPROM 23 that are used as an operation area of the ASIC 20 and the CPU 16 and a program storage area; a platen 25 that supports the printing paper 50; a transport roller 27 driven by the PF motor 1 to transport the printing paper 50; a pulley 30 attached to a rotating shaft of the CR motor 4; and a timing belt 31 driven by the pulley 30.
The DC unit 6 controls and drives the paper feed motor driver 2 and the CR motor driver 5 in response to a control instruction sent from the CPU 16 and outputs of the encoders 11, 13. Both the paper feed motor 1 and the CR motor 4 are DC motors.
FIG. 2 is a perspective view that illustrates configuration around the carriage 3 of the ink jet printer.
As shown in FIG. 2, the carriage 3 is connected to the carriage motor 4 by the timing belt 31 via the pulley 30, and driven to move in parallel with the platen 25 under guidance of a guide member 32. The carriage 3 has the recording head 9 projecting from its surface opposed to the printing paper and having a row of nozzles for releasing black ink and a row of nozzles for releasing color ink. These nozzles are supplied with ink from the ink cartridge 34 and release drops of ink onto the printing paper to print characters and images.
In a non-print area of the carriage 3, there is provided a capping device 35 for shutting nozzle openings of the recording head 9 when printing is not executed, and a pump unit 36 having the pump motor 7 shown in FIG. 1. When the carriage 3 moves from the print area to the non-print area, it contacts a lever, not shown, and the capping device 35 moves upward to close the head 9.
When any of the nozzle openings of the head 9 is clogged, or ink is forcibly released from the head 9 just after replacement of the cartridge 34, the pump unit 36 is activated while closing the head 9, and a negative pressure from the pump unit 36 is used to suck out ink from the nozzle openings. As a result, dust and paper powder are washed out from around the nozzle openings, and bubbles in the head 9, if any, are discharged together with the ink to the cap 37.
FIG. 3 is a diagram schematically illustrating configuration of the linear encoder 11 attached to the carriage 3.
The encoder 11 shown in Gig. 3 includes a light emitting diode 11a, collimator lens 11b and detector/processor 11c. The detector/processor 11c has a plurality of (four) photo diodes 11d, signal processing circuit 11e, and two comparators 11fA, 11fB.
When a voltage VCC is applied across opposite ends of the light emitting diode 11a through a resistor, light is emitted from the light emitting diode 11a. This light is collimated into parallel beams by the collimator lens 11b, and the beams pass through the coding plate 12. The coding plate 12 has slits in predetermined intervals (for example, in intervals of {fraction (1/180)} inch).
Parallel beams passing through the coding plate 12 enter into photo diodes lid through fixed slits, not shown, and are converted into electric signals. Electric signals output from these four photo diodes 11d are processes in the signal processing circuit 11e. Signals output from the signal processing circuit 11e are compared in the comparators 11fA, 11fB, and comparison results are output as pulses. Pulses ENC-A, ENC-B output from the comparators 11fA, 11fB are outputs of the encoder 11.
FIGS. 4A and 4B are timing charts showing waveforms of two output signals from the encoder 11 during normal rotation of the CR motor and during its reverse rotation.
As shown in FIGS. 4A and 4B, in both normal rotation and reverse rotation of the CR motor, the pulse ENC-A and the pulse ENC-B are different in phase by 90 degrees. The encoder 4 is so configured that the pulse ENC-A is forward in phase by 90 degrees relative to the pulse ENC-B as shown in FIG. 4A when the CR motor 4 rotates in the normal direction, i.e., when the carriage 3 is moving in its main scanning direction whereas the pulse ENC-A is behind in phase by 90 degrees relative to the pulse ENC-B as shown in FIG. 4B when the CR motor 4 rotates in the reverse direction. Then, one period T of these pulses corresponds to each interval of the slits of the coding plate 12 (for example, {fraction (1/180)} inch), and it is equal to the time required for the carriage 3 to move from a slit to another.
On the other hand, the rotary encoder 13 for the PF motor 1 has the same configuration as the linear encoder 11 except that the former is a rotatable disc that rotates in response to rotation of the PF motor 1, and the rotary encoder 13 also outputs two output pulses ENC-A, ENC-B. In ink jet printers, in general, slit interval of a plurality of slits provided on a coding plate of the encoder 13 for the PF motor 1 is {fraction (1/180)} inch, and paper is fed by {fraction (1/1440)} inch when the PF motor rotates by each slit interval.
FIG. 5 is a perspective view showing a part related to paper feeding and paper detection.
With reference to FIG. 5, explanation is made about the position of the paper detecting sensor 15 shown in FIG. 1. In FIG. 5, a sheet of printing paper 50 inserted into a paper feed inlet 61 of a printer 60 is conveyed into the printer 60 by a paper feed roller 64 driven by a paper feed motor 63. The forward end of the printing paper 50 conveyed into the printer 60 is detected by an optical paper detecting sensor 15, for example. The paper 50 whose forward end is detected by the paper detecting sensor 15 is transported by a paper feed roller 65 driven by the PF motor 1 and a free roller 66.
Subsequently, ink is released from the recording head (not shown) fixed to the carriage 3 which moves along the carriage guide member 32 to print something on the printing paper 50. When the paper is transported to a predetermined position, the terminal end of the printing paper 50 currently under printing is detected by the paper detecting sensor 15. The printing paper 50 after printing is discharged outside from a paper outlet 62 by a discharge roller 68 driven by a gear 67C, which is driven by the PF motor 1 via gears 67A, 67B, and a free roller 69.
FIG. 6 is a perspective view illustrating details of parts associated to paper feeding in a printer, where a paper feeding roller 65 has a rotation axis coupled to a rotary encoder 13.
With reference to FIG. 6 and FIG. 5, the parts in the printer associated to the paper feeding will now be described in details.
When a leading end of a printing paper 50, which has been inserted through a paper feed inlet 61 into a printer 60 by a sheet supplying roller 64, is detected by a paper detecting sensor 15, the paper feeding roller 65 and a follower roller 66 are cooperative in feeding the printing paper 50. The paper feeding roller 65 is provided on and about a small shaft 83 or a rotation axis of a large gear 67a engaged with a small gear 87 driven by a PF motor 1 while the follower roller 66 is provided in a holder 89 at its paper evacuating end in the context of a paper feeding direction, where the printing paper 50 from a paper supply source is pressed vertically.
The PF motor 1 is fitted in and secured to a frame 86 in the printer 60 by a screw 85, and the rotary encoder 13 is placed in a specified position around the large gear 67a while a character board 14 for the rotary encoder is connected to the smap shaft 83 or the rotation axis of the large gear 67a. 
After the printing paper 50, which has already been supplied by the paper feeding roller 65 and the follower roller 66 into the printer, passes over a platen 84 serving to support the printing paper 50, a paper evacuating gear 68 which is rotated by the PF motor 1 via a group of gears, the small gear 87, the large gear 67a, a medium gear 67b, a small gear 88, and a paper evacuating gear 67c, and a toothed roller 69 or a follower roller cooperatively presses and holds the printing paper 50 between them to further feed the printing paper 50 until it is evacuated from the paper outlet 62 to the outside of the printer.
While the printing paper 50 lies over the platen 84, a carriage 3 moves laterally in a space defined above the platen 84 along a guide member 32, and simultaneously, ink is injected from a recording head (not shown) fixed to the carriage 3 to print characters in the printing paper.
Now, an arrangement of a DC unit 6 will be described, which is a prior art DC motor control apparatus used to control a carriage (CR) motor 4 for such an ink jet printer as mentioned above, and additionally, a control method by the DC unit 6 will also be explained.
FIG. 7 is a block diagram showing an arrangement of the DC unit 6 serving as the DC motor control apparatus while FIGS. 8A and 8B are graphs illustrating time-varying motor current and motor speed of the CR motor 4 under control by the DC unit 6.
The DC unit 6 shown in FIG. 7 includes a position operator 6a, a subtracter 6b, a target speed operator 6c, a speed operator 6d, a subtracter 6e, a proportional element 6f, an integral element 6g, a differential element 6h, an adder 6i, a D/A converter 6j, a timer 6k, and an acceleration controller 6m. 
The position operator 6a detects rising edges and tail edges of the output pulses ENC-A and ENC-B of the encoder 11, then counts the number of edges detected, and operates the position of the carriage 3 from the counted value. This counting adds xe2x80x9c+1xe2x80x9d when one edge is detected while the CR motor 4 rotates in the normal direction, and adds xe2x80x9cxe2x88x921xe2x80x9d when one edge is detected while the CR motor 4 rotates in the reverse direction. Period of pulses ENC-A and period of pulses ENC-B are equal to the slit interval of the coding plate 12, and the pulses ENC-A and ENC-B are different in phase by 90 degrees. Therefore, the count value xe2x80x9c1xe2x80x9d of that counting corresponds to 1/4 of the slit interval of the coding plate 12. As a result, distance of the movement from the position of the carriage 3, at which the count value corresponds to xe2x80x9c0xe2x80x9d, can be obtained by multiplying the above count value by xc2xc of the slit interval. Resolution of the encoder 11 in this condition is xc2xc of the slit interval of the coding plate 12. If the slit interval is {fraction (1/180)} inch, then the resolution is {fraction (1/720)} inch.
The subtracter 6b operates positional difference between the target position sent from the CPU 16 and the actual position of the carriage 3 obtained by the position operator 6a. 
The target speed calculator 6c computes a target speed of the carriage 3 by referring to a positional deviation produced by a subtracter 6b. A result of the arithmetic operation is obtained by a multiply operation of the positional deviation by a gain KP. The gain KP varies depending upon the positional deviation. A value of the gain KP may be stored in a look-up table not shown.
The speed calculator 6d computes the speed of the carriage 3 on the basis of the output pulses ENC-A and ENC-B from the encoder 11. The speed is obtained in a manner as explained below. First, rising edges and tail edges of output pulses ENC-A, ENC-B of the encoder 11 are detected, and the duration of time between edges corresponding to xc2xc of the slit interval of the coding plate 12 is counted by a timer counter, for example. When the count value is T and the slit interval of the coding plate 12 is xcex, the speed of the carriage is obtained as xcex/(4T). Note here that operation of the speed is performed by measuring one period of output pulses ENC-A, e.g., from a rising edge to the next rising edge, by means of a timer counter.
The subtracter 6e operates speed difference between the target speed and the actual speed of the carriage 3 operated by the speed operator 6d. 
The proportional element 6f multiplies the speed difference by a constant Gp, and outputs its multiplication result. The integral element 6g cumulates products of speed differences and a constant Gi. The differential element 6h multiplies the difference between the current speed difference and its preceding speed difference by a constant Gd, and outputs its multiplication result. Operations of the proportional element 6f, the integral element 6g and the differential element 6h are conducted in every period of output pulses ENC-A of the encoder 11, synchronizing with the rising edge of each output pulse ENC-A, for example.
Outputs of the proportional element 6f, the integral element 6g and the differential element 6h are added in the adder 6i. Then, the result of the addition, i.e., the drive current of the CR motor 4, is sent to the D/A converter 6j and converted into an analog current. Based on this analog current, the CR motor 4 is driven by the driver 5.
The timer 6k and the acceleration controller 6m are used for controlling acceleration whereas PID control using the proportional element 6f, the integral element 6g and the differential element 6h is used for constant speed and deceleration control during acceleration.
The timer 6k generates a timer interrupt signal every predetermined interval in response to a clock signal sent from the CPU 16.
The acceleration controller 6m cumulates a predetermined current value (for example 20 mA) to the target current value every time it receives the timer interrupt signal, and results of the integration, i.e, target current values of the DC motor during acceleration, are sent to the D/A converter 6j from time to time. Similarly to PID control, the target current value is converted into an analog current by the D/A converter 6j, and the CR motor 4 is driven by the driver 5 according to this analog current.
The driver 5 has four transistors, for example, and it can create (a) a drive mode for rotating the CR motor 4 in the normal or reverse direction; (b) a regeneration brake drive mode (a short brake drive mode, which is the mode maintaining a halt of the CR motor); and (c) a mode for stopping the CR motor, by turning those transistors ON or OFF in accordance with outputs from the D/A converter 6j. 
Next explained is the performance of the DC unit 6, that is, the conventional DC motor control method, with reference to FIGS. 8A and 8B.
While the CR motor 4 stops, when a start instruction signal for starting the CR motor 4 is sent from the CPU 16 to the DC unit 6, a start initial current value I0 is sent from the acceleration controller 6m to the D/A converter 6j. This start initial current value I0 is sent together with the start instruction signal from the CPU 16 to the acceleration controller 6m. Then, this current value I0 is converted into an analog current by the D/A converter 6j and sent to the driver 5 which in turn start the CR motor 4 (see FIGS. 8A and 8B). After the start instruction signal is received, the timer interrupt signal is generated every predetermined interval from the timer 6k. The acceleration controller 6m cumulates a predetermined current value (for example, 20 mA) to the start initial current value Io every time it receives the timer interrupt signal, and sends the cumulated current value to the D/A converter 6j. Then, the cumulated current value is converted into an analog current by the D/A converter 6j and sent to the driver 5. Then, the CR motor is driven by the driver 5 so that the value of the current supplied to the CR motor 4 becomes the cumulated current value mentioned above, and the speed of the CR motor 4 increases (see FIG. 8B). Therefore, the current value supplied to the CR motor 4 represents a step-like aspect as shown in FIG. 8A. At that time, the PID control system also works, but the D/A converter 6j selects and employs the output from the acceleration controller 6m. 
Cumulative processing of current values of the acceleration controller 6m is continued until the cumulated current value reaches a fixed current value IS. When the cumulated current value reaches the predetermined value IS at time t1, the acceleration controller 6m stops its cumulative processing, and supplies the fixed current value Is to the D/A converter 6j. As a result, the CR motor 4 is driven by the driver 5 such that the value of the current supplied to the CR motor 4 becomes the current value IS (see FIG. 8A).
In order to prevent the speed of the CR motor 4 from overshooting, if the speed of the CR motor 4 increases to a predetermined value V1 (see time t2), the acceleration controller 6m makes a control to reduce the current supplied to the CR motor 4. At that time, the speed of the CR motor 4 further increases, but when it reaches a predetermined speed Vc (see time t3 of FIG. 8B), the D/A converter 6j selects the output of the PID control system, i.e., the output of the adder 6i, and PID control is effected.
That is, based on the positional difference between the target position and the actual position obtained from the output of the encoder 11, the target speed is operated, and based on the speed difference between this target speed and the actual speed obtained from the output of the encoder 11, the proportional element 6f, the integral element 6g and the differential element 6h act to perform proportional, the integral and the differential operations, respectively, and based on the sum of results of these operations, the CR motor 4 is controlled. These proportional, integral and differential operations are conducted synchronously with the rising edge of the output pulse ENC-A of the encoder 11, for example. As a result, speed of the DC motor 4 is controlled to be a desired speed Ve. The predetermined speed Vc is preferably a value corresponding to 70 through 80% of the desired speed Ve.
From time t4, the DC motor 4 reaches the desired speed, and the carriage 3 also reaches the desired constant speed Ve and can perform printing.
When the printing is completed and the carriage 3 comes close to the target position (see time t5 in FIG. 8B), the positional difference becomes smaller, and the target speed also becomes slower. Therefore, the speed difference, i.e., the output of the subtracter 6e becomes a negative value, and the DC motor 4 is decelerated and stops at time t6.
However, since the conventional motor control method and control apparatus electrically feed the motor until the subject to be driven by the motor (motor-driven subject) reaches its target stop position, they involved the problem that fluctuation in motor speed reflected on the positioning accuracy of the stop position of the subject to be driven, and if large, it degraded the positioning accuracy of the stop position of the subject to be driven.
Additionally, the conventional motor control method and control apparatus involved another problem explained below specifically.
In a printer using the conventional motor control apparatus having the above-explained structure, paper feeding is effected by the paper-feeding roller 65 driven by the PF motor 1 and the follower roller 66 as already explained with reference to FIGS. 5 and 6. The follower roller 66 is configured to urge the paper sheet 50 onto the paper-feeding roller 65 during the paper feeding motion with the aid of the spring 80 as shown in FIG. 9.
On the other hand, there is an increasing demand for printing over a wider area of the paper sheet 50 including portions nearest to its perimeters. For this purpose, it is necessary to hold a perimeter of the sheet 50 with the paper feeding roller 65 and the follower roller 66 within a predetermined extent x (for example, within 0.25 mm from the front to the back of a line connecting the centers of the paper feeding roller 65 and the follower roller 66).
However, in printers using conventional motor control apparatuses, since the follower roller 66 is urged toward the paper feeding roller 65 with a spring 80, if the perimeter of the sheet 50 is positioned within the predetermined extent while the sheet 50 is transported, a force F (see FIG. 10) tending to send out the sheet 50 is applied to the sheet 50 from the spring 80. Therefore, the sheet 50 is sent out from between the paper feeding roller 65 and the follower roller 66, and printing on the sheet 50 near the perimeter is not possible.
It is therefore the first object of the invention to provide a motor control apparatus ad a motor control method having a high positioning accuracy for the stop position of a subject to be driven by a motor motor-driven subject).
A motor control apparatus according to the invention is characterized in comprising a stop position prediction controller for instructing deenergization of a motor a predetermined period of time later than arrival of a subject to be driven by the motor at a predetermined position, the predetermined period of time corresponding to a predetermined condition upon arrival of the subject to be driven at the predetermined position, and the predetermined position being at a predetermined distance before a target stop position of the subject to be driven.
In a more specific configuration, the motor control apparatus according to the invention is characterized in comprising a stop position prediction controller for instructing deenergization of a motor a predetermined period of time later than arrival of a subject to be driven by the motor at a speed measuring position, the predetermined period of time corresponding to a current speed of the motor upon arrival of the subject to be driven at the speed measuring position, and the speed measuring position being at a predetermined distance before a target stop position of the subject to be driven. This configuration makes it possible to prevent influences to the positioning accuracy for the stop position of the subject to be driven from fluctuations of the motor speed and improve the positioning accuracy for the stop position of the subject to be driven.
The predetermined period of time may be determined to be in an extent that ensures deenergization of the motor is instructed before arrival of the subject to be driven at the target stop position.
In a furthermore specific configuration, the motor control apparatus according to the invention is characterized in comprising a position calculator for calculating and outputting a current position of a subject to be driven by a motor on the basis of encoder pulses output from an encoder in response to rotation of the motor; a speed calculator for calculating and outputting a current speed of the motor on the basis of the encoder pulses; and a stop position prediction controller for outputting a deenergization instruction signal, which instructs deenergization of the motor, a predetermined period of time later than arrival of the subject to be driven at a speed measuring position, the predetermined period of time corresponding to the current speed of the motor upon arrival of the subject to be driven at the speed measuring position, and the speed measuring position being at a predetermined distance before a target stop position of the subject to be driven.
The predetermined period of time is determined to be in an extent that ensures the deenergization instruction signal is output before arrival of the subject to be driven at the target stop position.
The motor control apparatus according to the invention may further comprise a data storage portion for storing data on relations between the current speed of the motor upon arrival of the subject to be driven at the speed measuring position and the predetermined period of time.
The stop position prediction controller may measure the predetermined period of time by counting the number of the encoder pulses. Alternatively, the stop position prediction controller may measure the predetermined period of time by counting the number of pulses of a predetermined clock.
Destination of the deenergization instruction signal may be a drive signal generator that generates a drive signal for rotatably driving the motor.
The predetermined period of time is determined to a value that ensures the subject to be driven stops at the target stop position.
The predetermined period of time varies substantially in reverse proportion to the current speed of the motor upon arrival of the subject to be driven at the speed measuring position.
A motor control method according to the invention is characterized in instructing deenergization of a motor a predetermined period of time later than arrival of a subject to be driven by the motor at a predetermined position, the predetermined period of time corresponding to a predetermined condition upon arrival of the subject to be driven at the predetermined position, and the predetermined position being at a predetermined distance before a target stop position of the subject to be driven.
In a more specific configuration, the motor control method according to the invention is characterized in instructing deenergization of a motor a predetermined period of time later than arrival of a subject to be driven by the motor at a speed measuring position, the predetermined period of time corresponding to a current speed of the motor upon arrival of the subject to be driven at the speed measuring position, and the speed measuring position being at a predetermined distance before a target stop position of the subject to be driven. This configuration makes it possible to prevent influences to the positioning accuracy for the stop position of the subject to be driven from fluctuations of the motor speed and improve the positioning accuracy for the stop position of the subject to be driven.
In a furthermore specific configuration, a motor control method according to the invention is characterized in comprising a first process for measuring a current position of a subject to be driven by a motor and monitoring whether the subject to be driven has reached a speed measuring position at a predetermined distance before a target stop position of the subject to be driven; a second process for measuring the current speed of the motor upon arrival of the subject to be driven at the speed measuring position; a third process for determining a predetermined period of time corresponding to the current speed of the motor upon arrival of the subject to be driven at the speed measuring position; and a fourth step for instructing deenergization of the motor the predetermined period of time later, than arrival of the subject to be driven at the speed measuring position.
For the purpose of determining the predetermined period of time, data may be previously collected and stored concerning relations between the current speed of the motor upon arrival of the subject to be driven at the speed measuring position and the predetermined period of time.
The predetermined period of time is determined to be in an extent that ensures deenergization of the motor is instructed before arrival of the subject to be driven at the target stop position.
The predetermined period of time is determined to a value that ensures the subject to be driven stops at the target stop position.
The predetermined period of time varies substantially in reverse proportion to the current speed of the motor upon arrival of the subject to be driven at the speed measuring position.
The predetermined period of time may be measured by counting the number of the encoder pulses. Alternatively, The predetermined period of time may be measured by counting the number of pulses of a predetermined clock.
In the motor control apparatus and the motor control method according to the invention, the motor to be controlled may be a DC motor, a stepping motor, AC motor.
Further, the motor to be controlled may be a paper feeding motor of a printer or a carriage motor of a printer.
The second object of the invention is to provide a motor control apparatus and a motor control method for controlling paper feeding in a manner enabling printing over a wider area of a sheet to near its perimeters.
The motor control apparatus according to the invention includes a position detector for detecting the position of paper driven by a paper feeding motor on the basis of output pulses of an encoder that rotates in response to rotation of the paper feeding motor; and a drive controller for controllably driving the paper feeding motor by additionally applying a current value to the paper feeding motor on the basis of a target value of the paper feeding amount and an output of the position detector, and it is characterized in generating a current value signal that causes the paper to stop or rotate in the opposite direction from a normal paper feeding direction in response to output pulses of the encoder after arrival of the paper feeding amount reaches the target value, and controllably driving the paper feeding motor with the driving controller in response to the current value signal.
The motor control apparatus according to the invention may further comprise a pulse counter for counting output pulses of the encoder during movement of the paper in the reverse direction from the normal paper feeding direction after the feeding amount of the paper reaches the target feeding value and for outputting an instruction signal when the count value reaches a predetermined value; and a current value signal generator for generating the current value signal upon receipt of the instruction signal or during movement of the paper in the reverse direction from the normal paper feeding direction.
The current value signal generator may include a detector for detecting whether the paper remains still, or is moving in the reverse direction from the normal paper feeding direction, in response to outputs from the encoder; and a current value determiner for determining and outputting the current value signal in response to the instruction signal or a result of detection by the detector.
The current value determiner may output the same current value signal as the latest current value signal when the paper remains still, and generate a current value signal that is smaller in absolute value than the latest current value signal but equal in sign when the paper is moving in the reverse direction from the normal paper feeding direction.
Further, the motor control method according to the invention is characterized in comprising the steps of: generating a current value signal causing paper to stop or move in the opposite direction from a normal paper feeding direction in response to output pulses given from an encoder after the paper feeding amount reaches a target feeding value, said encoder rotating in response to ration of a paper feeding motor; and controllably driving said paper feeding motor in response to said current value signal.
The step of generating the current value signal may include the steps of: counting output pulses of the encoder during movement of the paper in the reverse direction from the normal paper feeding direction; and generating the current value signal when the count value of the output pulses reaches a predetermined value.
Furthermore, the recording medium of a computer program according to the invention is characterized in having recorded a computer program for executing in a computer system one of the above-summarized motor control methods according to the invention.